This invention relates to the catalytic oxidation of phenols to 1,4-benzoquinones. More particularly, the invention relates to catalyst compositions for the oxidation of phenols to 1,4-benzoquinones in the gas phase with oxygen.
The compound 1,4-benzoquinone is beneficially used as an oxidizing and tanning agent. Moreover, 1,4-quinones are useful intermediates for making hydroquinones, which find utility as antioxidants, reducing agents, and polymer intermediates.
Benzoquinones are usually manufactured from the corresponding phenols by treating the phenols with oxidizing agents. For example, phenol may be oxidized using sodium dichromate in an aqueous sulfuric acid medium. Such methods, however, have the disadvantage that they produce solid metal oxides as by-products and require stoichiometric amounts of the oxidant. An additional disadvantage is that the benzoquinone products formed are mixed with other compounds and must be separated to obtain a substantially pure form thereof.
It is desirable to have a commercial process which may be used to manufacture benoquinones in significant yield and with a high degree of purity by a direct catalytic oxidation of the corresponding phenols. While it is known that phenols can be oxidized directly to the corresponding benzoquinones in the presence of a copper-containing catalyst, the process is carried out in solution, with the inherent problem of separating the products from the solvent and recycling of the catalyst. The present invention provides a heterogeneous catalyst for the oxidation of phenols to the corresponding benzoquinones in the gas phase, thereby eliminating the problem of solvent-product separation and catalyst recycle.